1. Field of the Invention
The present invention relates to a method of production of activated carbon for removal of mercury gas, in particular, relates to a method of production of activated carbon which impregnates activated carbon with iodine and sulfur so as to raise the adsorption capacity of mercury.
2. Description of the Related Art
Mercury and other heavy metal ingredients, as seen in the RoHS directive of the European Union etc., requires strict handling and is restricted in use from the viewpoint of health and pollution prevention. However, mercury is known to be produced at the time of burning coal for generating power and from the process of refining of crude oil and has become a problem in treatment of the smoke and dust. Further, mercury is being used for fluorescent lamps or batteries, so safe disposal of used products and waste is being viewed with even more importance than in the past.
In general, for adsorption of mercury vapor, much use is made of an adsorbent using a chemical of iodine, potassium iodide, or other halogen or halide as an adsorption species. This adsorbent uses iodine as a material, so has the problem of a ballooning prime cost of manufacture. Therefore, as a more inexpensive mercury adsorbent, activated carbon carrying sulfur has been proposed (see PLT's 1, 2, 3, etc.) For example, activated carbon and sulfur particles are mixed and the mixture heated at 110 to 400° C. to obtain an adsorbent. However, with an adsorbent of only activated carbon and sulfur, the adsorption performance per unit weight is insufficient.
Separate from this flow, a mercury gas adsorbent comprised of activated carbon which carries sulfur and an iodide or bromide has been proposed (see PLT 4 etc.) According to the method of preparation of an absorbent of Example 1 disclosed on page 2 of that PLT 4, the activated carbon is uniformly sprayed with a predetermined amount of an aqueous solution in which a bromide, iodide, sulfate, or nitrate has been dissolved, then a predetermined amount of sulfur particles is mixed in and the result is heated in the air at 110° C.
In general, it is known that the reaction speed when mercury and iodine bond is faster than the reaction speed when mercury and sulfur react. In particular, PLT 4 uses both iodine and sulfur, so can be said to raise the adsorption efficiency of mercury while utilizing the difference in the reaction speed. However, iodine is higher in price compared with sulfur, so when hoping for the desired mercury adsorption capability, regardless of what one wants, the material costs end up rising.